BRITAIN ON HIGH ALERT WHILE PUSHING FOR N. IRELAND DEAL

A week after a bomb set by the Irish Republican Army (IRA) shattered Northern Ireland's cease-fire, the British government is hoping for the best - but preparing for the worst.

At the same time that Britain and Ireland are renewing their diplomatic push for peace talk, armored vehicles and troops with body armor have returned to Belfast, Northern Ireland's capital. As of today, the number of British troops in Northern Ireland will return to 17,000 - what it was before the cease-fire began in 1994.

Gerry Adams, the president of Sinn Fein, the political wing of the IRA, has called for urgent talks with the British and Irish prime ministers. Yet his authority as a peacemaker has been heavily compromised by the bombing. In a statement published yesterday, the IRA confirmed that its cease-fire had ended. It suggested it would not necessarily heed any Sinn Fein advice.

John Hume, the moderate Catholic leader who is widely seen as crucial in rescuing the peace process, this week called for referendums in both parts of Ireland as a possible way out of the crisis. He proposes that voters in the Irish Republic and Northern Ireland be asked two questions: whether they renounce violence, and whether they want all-party talks.

Ian Paisley, the usually strident leader of the Democratic Unionist Party, surprised his Protestant supporters by saying he was ''willing to listen to what Mr. Hume has to say.''

Major and Irish Prime Minister Bruton are seeking a compromise over how to arrange all-party talks.

Before the bomb attack Feb. 9 and immediately afterward, London held out for elections to a negotiating body, a move that many Catholics saw as a stalling tactic and that Bruton last weekend said would be ''like pouring petrol on a fire.''

But by early this week, the mood had changed. Major told the British Parliament he would ''shut no doors'' in the pursuit of peace, and his officials said it was possible for elections to be preceded by so-called proximity talks in the style of the no-nonsense negotiations in Dayton, Ohio, where Bosnia's factions hammered out a peace deal last fall.

Mr. Bruton added that he and Major were now ''willing to involve Sinn Fein'' in the political process, but Adams must first ''say the campaign of violence is over.'' But getting Adams to that point will be difficult, both governments concede.

Paul Bew, a professor of politics at Queen's University in Belfast, argues that with Adams considerably discredited, a way is open for a deal ''between constitutional nationalists in both parts of Ireland.'' Mr. Bew applauds the referendum idea launched by Hume, who heads the moderate Social Democratic and Labour Party, as ''evidence of his commitment to democratic methods.''

If Hume were to accept a compromise deal involving proximity talks, Bew says, elections - and possibly also a referendum - he could still turn out to be a key figure in attempts to move ahead again from the bombing Feb. 9 and put peace talks back on track.